Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor. A housing supports the drive motor and head actuator, and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a suspension that connects the slider to the actuator. The slider flies over the disk surface as a consequence of a balance of the spring force from the suspension and the air pressure generated by the velocity of the rotating disk. In a variation of the conventional air bearing, a combined air and liquid bearing supports the slider, which is in very close proximity or actual contact with a relatively thin lubricant film on the disk. Disk drives of this type are described in U.S. Pat. No. 4,901,185 assigned to Toshiba and U.S. Pat. No. 5,202,803 assigned to IBM.
The most common form of disk drive actuator is a rotary actuator that moves the head carriers in a nonlinear, generally arcuate path across the disk surfaces. Typically, there are two head carriers per disk, one for each of the "top" and "bottom" disk surfaces, that are attached to the actuator so that the carriers move in unison on the opposite surfaces of the disk. The conventional arrangement for reading and writing data is the well-known "cylinder mode". In this arrangement, continuous data is written by the top head writing to the top disk surface, followed immediately by the bottom head writing to the corresponding track in the same "cylinder" on the bottom disk surface. Cylinder mode operation allows reading and writing on a data track on one data surface, to be immediately followed by reading or writing on the corresponding data tracks (i.e., the data tracks in the same cylinder) on other data surfaces with little or no repositioning of the actuator. In disk drives that use noncylinder mode, there is no requirement that the heads on different disk surfaces be generally aligned with one another because data is typically written by writing first to one disk surface on adjacent tracks and then followed by writing to other disk surfaces on adjacent tracks.
Because the rotary actuator moves in an arcuate path, the sensing ends of the heads are not always aligned perpendicular to the data tracks, but are skewed relative to the tracks, the amount of skew varying with radial position. Recent disk drives use dual-element heads, i.e., an inductive coil element for writing and a magnetoresistive (MR) element for reading. One problem that arises with dual-element heads in rotary actuator disk drives with inherent skew is that because the two elements are spaced from one another in a direction perpendicular to the trailing end of the carrier, a rotary actuator is not able to maintain both elements in simultaneous alignment with the data tracks due to the inherent nonlinear path across the disk surface. To compensate for this, dual-element heads are typically fabricated with the read and write elements slightly offset from one another in a direction parallel to the trailing end of the carrier, the amount of offset being determined by the average skew of the heads. However, this solution is only optimal at one specific angular position of the rotary actuator and becomes unacceptable at high track densities where the data tracks are very closely spaced. An additional problem with dual-element heads in both rotary actuator disk drives and linear actuator disk drives is that because the elements are closely spaced on top of one another on the trailing end of the slider so that both elements can be aligned with the same data track, the magnetic field from the inductive write element can alter the magnetization state of the nearby MR read element.
Side-by-side, dual-element heads have been proposed to address these problems. In a side-by-side head, the write gap (i.e., the sensing end) of the inductive coil write element and the MR sensing film of the MR read element are located in the same plane on the trailing end of the slider but are spaced apart from one another in a direction parallel to the slider trailing end. In this design, the read and write elements are not simultaneously located over the same track so it is necessary for the actuator to move the slider if read and write operations are to take place sequentially on the same track. Side-by-side, dual-element heads are described in U.S. Pat. Nos. 5,229,901 assigned to DEC and 4,729,048 assigned to Sony. In these designs, a single write element and a single read element are located on the trailing end of the slider. However, since the read and write elements on the top data surface of the disk must be aligned with their counterparts on the bottom data surface of the disk if the disk drive is to operate in cylinder mode, the side-by-side head associated with the top surface of the disk must be the mirror image of the side-by-side head associated with the bottom surface of the disk. The result is that two different types of heads must be fabricated: one for the top surfaces of the disks and the other for the bottom surfaces of the disks. This complicates the head manufacturing process and disk drive assembly process.
An additional problem with both conventional dual-element heads and side-by-side, dual-element heads is that if either the read element or write element is determined to be bad after manufacturing, the entire head carrier is rejected.
What is needed is a slider with a side-by-side read/write head structure that can be manufactured at a higher yield and can function as a single common part for use on both top and bottom data surfaces, thereby resulting in a disk drive with identical side-by-side heads on all disk surfaces.